1. Field of the Invention
The present invention relates to the art of opening blast furnace tap holes and to blast furnace tap hole drills, and more particularly to a unique quick connect-disconnect threaded coupling for use within the drill rod assembly which will not only permit a quick connection and disconnection of the drill rod components but will also permit the coupling and uncoupling to be quickly performed by hand without the need for a wrench or wrenches. The coupling of this invention will also prolong the useful life of the components connected thereto and will even provide a self-connecting and disconnecting capability upon proper activation of the tap hole drill.
2. Summary of the Prior Art
It is well known that the hearth of an iron blast furnace is provided with a tap hole, commonly referred to as an "iron notch" through which molten iron, usually referred to as "hot metal", is drawn off at periodic intervals during the blast furnace campaign. During a normal campaign, such tapping must be done on an average of five to twelve times daily as the blast furnace hearth becomes filled with molten iron and slag. After the blast furnace has been tapped; i.e., the molten hot metal and slag drained therefrom, the tap hole or iron notch is plugged with clay or "mud" which will harden and seal the tap hole until the next time the blast furnace is tapped.
In accordance with usual practices, a special drill is utilized to open a tap hole; i.e., drill a passageway through the hardened clay plugging the iron notch for the purposes of tapping the blast furnace. Such blast furnace tap hole drills are normally pneumatically or hydraulically operated rotary percussion drills comparable to the rock drills utilized in the mining industry. Such drills impart both a rotary and an impact force on an elongated drill rod having a rock drill bit at the end towards the iron notch.
The base support for the blast furnace tap hole drill is normally secured to the floor, a structural column, or some solid base structure and is provided with suitable linkage members and remote controls so that the blast furnace tap hole drill can be remotely operated from a safe distance. Pursuant to such a remote operation, the tap hole drill is operated to move the drill into the proper position for drilling the tap hole, then operated to drill the tap hole, and thereafter, moved back away from the tap hole and heat of the emerging hot metal, where the drill can be serviced and prepared for the next tap.
To prepare the blast furnace tap hole drill for each succeeding tap, it is always necessary to replace the drill bit, if not the drill rod or a portion thereof. This is because the temperature of the blast furnace hot metal, being about 2700.degree.-2800.degree. F., severely erodes the drill bit after it drills through the clay plug and enters the bath of molten hot metal. In addition, once the tap hole is drilled, the ferrostatic head of hot metal within the blast furnace will cause the hot metal to emerge through the tap hole around the drill bit and drill rod before the drill rod and bit can be withdrawn from the tap hole. Often times, the drill bit will not only be severely eroded but the portion remaining will virtually be "welded" or "galleded" to the end of the drill rod to which it had previously been removably attached. In such an event, it will be impossible to remove the drill bit from the drill rod to replace a new drill bit; and accordingly, it then becomes necessary to replace the entire drill bit and adjoining drill rod or drill rod component to which it is welded or galleded.
To reduce the expense of replacing the entire drill rod and bit assembly, it has become common practice to utilize a drill rod extension, which is merely a removable end portion of the drill rod, typically from 18 to 30 inches in length, fitted between the elongated rearward portion of the drill rod and the drill bit. Therefore, when the drill bit becomes welded or galleded to the drill rod extension bar, or the extension bar otherwise damaged, the bit and extension bar can be replaced without the need for replacing the entire drill rod assembly.
While in some situations it may be possible to remove one drill rod component from another, such as an extension bar from a drill rod, it often happens that the threaded portions are damaged and not reusable once separation is achieved. This is because the threaded portions of the extension bar and drill rod, but for the drill bit itself, are perhaps the surfaces most vulnerable to damage as a result of the heat to which the thin threads are exposed, in combination with the wrench imposed torque stresses on the threads, which may virtually strip or otherwise damage the threads sufficiently to render them useless.
It has long been appreciated that the use of more robust threading will render the threads less susceptible to damage. In fact, conventional rock drilling drill rod assemblies are normally provided with one or another of the well known heavy threadings; i.e., rope threads, trapezoidal threads, double entry threads, and Hi-Leed threads. All these well known threads provide a rather heavy thread section to better withstand the rotary and impact forces to which they are subjected. Since these specialized threads must normally be machined into the drill rods by the manufacturer, they are naturally more expensive than those having conventional pipe threading. Their added cost appears to be justified, in so far as conventional rock drills are concerned, in adding significantly to the life of the drill rods.
While it is also known to utilize the above-noted heavy threads in blast furnace tap hole drill rod assemblies, the use of conventional pipe threads is far more common with regard to blast furnace tap hole drills. This is because the average useful life of drill rods used in a blast furnace tap hole drill is quite short regardless of the threads used, so that the added cost is not normally justified. Indeed, blast furnace tap hole drill rods are often damaged and in need of replacement for reasons other than damage to the threads, such as being welded to the extension bar, for example. Therefore, because blast furnace tap hole drill rods are in the nature of a consumable item, as compared to rock drill rods, the use of conventional pipe threading is usually preferred.
In addition to the above problems associated with efforts to salvage as much of the drill rod assembly as possible for reuse as a means of cost savings, it should be appreciated that the manual task of preparing the tap hole drill for each succeeding tap is a most unpleasant one and does expose the workers; i.e., the tap crew making the repairs, to a hazardous environment. The environment in which the tap crew must work to replace the damaged drill rod assembly components is, of course, reasonably close to the blast furnace, which has an interior temperature well in excess of 3,000.degree. F. Also, the atmosphere adjacent to the blast furnace is far from pleasant, as it usually contains noxious gases that manage to escape from the furnace. In addition, the site is usually adjacent to the runner through which the blast furnace had just been tapped. This runner, consisting of a fire-brick lined trough usually built into the floor adjacent to the furnace, will retain an excessive amount of heat for a rather long period of time after the hot metal has been tapped. Obviously, the tap hole drill rod assembly components themselves will also retain an exceptional amount of heat, and will be too hot to handle without protective gloves and additional protective clothing. Therefore, the tap crew is always anxious to prepare the tap hole drill rod assembly as quickly as possible in an effort to spend as little time as possible in the rather unpleasant atmosphere in which they must work. Because of the heat to which the drill rod components were subjected, however, it often happens that the thread connections are very tightly bonded together, often requiring three or four men with pipe wrenches working a considerable amount of time to disconnect a coupling. This is true for the heavy rock drill threaded connections (as noted above) as well as those utilizing conventional pipe threads.
While it would be helpful to delay the tap hole drill repair effort for a period of several hours to permit the site and drill rod components to cool more significantly, this is not possible because the tap-to-tap period may be as short as two hours. Therefore, it is deemed essential that the tap hole drill be prepared for the next tap as soon as the work can be achieved to assure that the drill will be ready for use when the furnace is ready to be tapped. Indeed, any delay in tapping the furnace after it is ready to be tapped will constitute a very costly delay to the overall operation of the facility by reducing blast furnace yield.